One of the therapeutic methods for cancers (malignant neoplasms), an intractable disease, includes so-called cancer immunotherapy that causes regression of cancer cells by utilizing an immune system of individual patients. The important point in this method is how to make the immune system recognize the cancer cells as foreign matter and induce immune cells that are aggressive to the cancer cells.
Key immune cells involved in anti-tumor immunity include a T cell expressing cell surface protein CD8 (CD8+ T cell) and a T cell expressing cell surface protein CD4 (CD4+ T cell). CD8+ T cells are T cells that, when activated, lyse a cell presenting antigens bound to an HLA class I molecule (cytotoxic T lymphocyte; CTL). CD4+ T cells are cytokine-secreting Th cells, which, upon being activated by macrophages and/or dendritic cells that present antigens on MHC class II molecules, exert a helper function for inducing and maintaining CD8+ T cells. In addition, Th cells are known to be classified by the type of cytokines secreted thereby, into Th1 cells (producing IFN-γ, etc.), Th2 cells (producing IL-4, etc.), and Th0 cells (having a low cytokine-producing ability or producing both IFN-γ and IL-4), and the roles of each cell are now being elucidated. Further, CD4+ T cells can show an effector function by their indirect mechanism against MHC class II molecule-negative tumors (MHC class II-tumors), for example, by activation of macrophages or via killer T cells or NK cells, or by their direct mechanism against MHC class II molecule-positive tumors.
Previous studies of T cells in human cancer immunotherapy have mainly focused on identification and induction of CD8+ HLA class I-restricted CTL response (Patent Literature 1). As for CD4+ T cells, the identification of tyrosinase, a cancer antigen, and its epitope to CD4+ T cells (helper epitope) has been reported (Patent Literature 2). Tyrosinase, which is expressed in normal cells and tumor cells of the melanocyte lineage and shown to be a specific target for CD4+ melanoma-reactive T cells, is the melanoma-associated and tissue-specific antigen that binds to MHC class II molecules (Non-Patent Literature 1). However, since tyrosinase is expressed only in limited types of tumors, it can hardly be said to be a promising cancer antigen in cancer immunotherapy.
Some of the present inventors have focused on the gene family, which is called MAGE, encoding tumor-specific antigens recognized by CD8+ T cells. One of polypeptide fragments derived from MAGE-A4 proteins among the family members has been found to be useful as a cancer vaccine peptide (helper epitope) (Patent Literature 3). However, because the type of cancers in which the MAGE-A4 protein is expressed is limited, there are still high expectations for the creation of a new polypeptide capable of inducing an immunological response against more numerous types of cancers.
On the other hand, WT1 protein is a protein, which is encoded by Wilms' tumor gene WT1 that is highly expressed in leukemia and various solid cancers. The WT1 protein is expected to be a candidate for cancer vaccine peptides, and a number of helper epitopes and killer epitopes derived from the WT1 proteins have been reported by many researchers. The WT1 protein is a typical example of cancer-related proteins (Patent Literatures 4 to 6, Non-Patent Literatures 1 to 3).
Further, immunological response induced by such a helper epitope and a killer epitope is controlled (restricted) by the polymorphism of the HLA gene (see “HLA-restriction” described later in Tables 1 to 5). It is also known that there are differences in the occurrence of, or in the strength of immunological responses by the helper epitope and killer epitope even among T cells derived from patients with the same HLA alleles. Thus, polypeptides capable of inducing a stronger immunological response against more numerous types of cancers by stimulating numerous T cells of different derivation have been desired.
In this regard, the present inventors have developed a long-chain polypeptide obtained by binding one helper epitope and one killer epitope (a helper/killer-hybrid epitope long peptide; H/K-HELP), and it has also been elucidated that by using this H/K-HELP, antigen-specific immunological response (production of antigen-specific CTL and Th cell) can be more efficiently induced compared with the case of using a mixture of the helper epitope and the killer epitope (Non-Patent Literature 4). In addition, with respect to such H/K-HELP, it has also been demonstrated by the present inventors that when H/K-HELP prepared by binding one helper epitope derived from the MAGE protein and one killer epitope derived from the MAGE protein is administered to a human patient with colon cancer that has spread to the lungs, a specific immunological response against the MAGE is strongly induced to result in a significant reduction of the tumor growth and CEA tumor marker in the patient (Non-Patent Literatures 4 and 5).